His plan was to make his neighbour Mr Horner suffer in the same way by sabotaging his heating, but a fault in his boiler meant that the automatic fail-safe system did not work and the neighbour's house filled with gas.

Police found Mr Horner dead on his living room floor wearing just underpants and with the heating turned up to 60C.

Tests showed that the fumes would have become fatal in his kitchen within 14 minutes of the boiler being switched on, with the carbon monoxide spreading to other rooms shortly afterwards.

Burgess, 38, of Newlyn, admitted manslaughter and was jailed for two years and eight months by Judge Geoffrey Mercer QC, at Exeter Crown Court.

He wants to express his very deep regret. He is profoundly sorry. His intention was to stop the boiler working and that is what would have happened but for the tragic coincidence of the faultKate Brunner QC

He told him: "You accept your unlawful and dangerous act in interfering with the flue of Mr Horner's boiler in the way you did caused his death. He had serious health issues and you knew of his disability and vulnerability.

"Mr Horner was your neighbour and had been your friend but you had fallen out and you acted to get your own back against a perceived grievance that he was the cause of the loss of your heating.

"You did what you did deliberately. You went to considerable lengths and you knew what you were doing. Of crucial importance is that you had no intention of doing any physical harm.

"Your plan was simply to stop his boiler from working and make him cold. I accept your remorse is genuine and your culpability is at the lower end."

Mr Paul Dunkels QC, prosecuting, said there was a background of ill feeling with accusations of theft and a previous confrontation at a bus stop.

Mr Horner suffered from Huntingdon's Disease and had heart problems, both of which restricted his mobility.

He returned home after visiting friends for Christmas dinner in 2015 to find his flat was cold because the gas was turned off at the outside meter.

He turned it on again but when he woke up on Boxing Day it had been turned off again and he was trapped inside because all his locks had been superglued and filled with foam.

Police freed him and visited Burgess. They found dents in the communal wall where he had hit it with a hammer and warned him to leave Mr Horner alone.

A friend alerted the police on December 29 and Mr Horner was found dead in his living room. The true cause only emerged when police found the flue blocked by a large potato and expanding foam.

Traces of foam were found on Burgess's clothing, his fingerprints were on an empty can in his garden and a partial DNA match was found on the potato.

Mr Dunkels said a safety device should have made the boiler cut out rather than carry on pumping out carbon monoxide but a cap had been removed.

Kate Brunner QC, defending, said Burgess suffers from paranoid schizophrenia which led him to blame his neighbour for the theft of his gas cards.

She said: "He wants to express his very deep regret. He is profoundly sorry. His intention was to stop the boiler working and that is what would have happened but for the tragic coincidence of the fault.

"He did not intend or foresee any harm. He could not perceive the boiler's safety system would fail. His mental illness may go some way to explaining his bizarre actions."